JP6534369B2 - Ground fault detection device for voltage type inverter - Google Patents

Description

  Embodiments of the present invention relate to a ground detector of a voltage type inverter.

  FIG. 3 is a ground fault detection circuit of a conventional ground fault detection apparatus for a voltage type inverter. In the illustrated example, only one phase is described. When the ground fault 73 occurs at the inverter output side cable point, the ground fault current flowing from the smoothing capacitor C1 returns to the smoothing capacitor C1 through a path indicated by a ground fault current Ig1 → Ig2 → Ig3 → Ig4 → Ig5.

  In the case of the illustrated example, a ground fault is detected by detecting a voltage Eg (Eg = R1 × Ig5) generated when the ground current Ig5 flows through the resistor R1, and the ground is detected when the Eg exceeds the set voltage. It is detected as a fault. The other phases are also detected.

  In addition, the insulation degradation diagnostic apparatus which detects the zero phase current of an electrical path is known as a method of diagnosing the insulation degradation of the electrical path connected between the inverter apparatus and the load apparatus by which inverter drive is carried out (for example, patent documents 1)).

  In addition, a distribution line ground fault detection method and a distribution line ground fault protection device are known (see, for example, Patent Document 2).

WO2011-129218 gazette JP-A-3-230721

  However, the method described in Patent Document 1 requires a path for detecting a leakage current, such as installing a power supply neutral point of an inverter input to find a portion where insulation deterioration has occurred, so that the method in the isolated circuit Ground fault current can not be detected. In addition, a complex detection circuit is required, for example, a detector matching the main circuit cable is required to detect the zero-phase current of the inverter output.

  Further, the method described in Patent Document 2 has a problem that it is difficult to find a minute current because a zero-phase detector with a large diameter is required according to the main circuit cable in order to detect the zero-phase current of the main circuit.

  The present invention has been made to solve the above-mentioned problems, and in a configuration in which an inverter and a motor are connected by a shielded cable, zero-phase current (zero-phase current of three-phase shielded wire) flowing in the shielded wire of this shielded cable By monitoring the occurrence of a ground fault even in an ungrounded system, and since the current flowing through the shield is a minute current, the zero-phase current detection sensor can also be made small, and a simple configuration can be obtained. It is an object of the present invention to provide a ground fault detection device of a voltage type inverter capable of ground fault detection in an ungrounded system.

  In order to achieve the above object, a ground fault detection device for a voltage type inverter according to claim 1 of the present invention comprises an inverter for connecting an output terminal of an inverter unit and a power input terminal of a motor with a shield cable to drive the motor. A ground fault detection device for a drive motor, wherein the power input terminal side shield wire of the motor is connected to the ground terminal of the motor body, and the ground terminal of the motor body, the output terminal side shield wire of the inverter unit and the inside of the inverter A current sensor that connects a ground bus with a ground wire, grounds the ground terminal of the ground bus, but does not ground the ground terminal of the motor body, and detects a zero-phase current flowing in the output terminal side shield wire of the inverter unit And a ground fault detection unit that monitors a zero-phase current detected by the current sensor and detects a ground fault.

  According to the present invention, in the configuration in which the output terminal of the inverter unit and the power input terminal of the motor are connected by the shield cable, the zero-phase current (zero-phase current of the three-phase shield wire) flowing in the shield wire of this shield cable is monitored. This makes it possible to confirm the occurrence of a ground fault even in an ungrounded system in which the motor side is not grounded, and since the current flowing through the shield is a minute current, the zero-phase current detector can also be configured to be small. It is possible to provide a ground fault detection device of a voltage type inverter capable of ground fault detection in an ungrounded system with a simple configuration.

FIG. 2 is a circuit diagram of an inverter unit provided with a ground fault detection unit according to a first embodiment. FIG. 7 is a diagram for explaining the operation of the ground fault detection unit in FIG. 1 when a ground fault occurs. The circuit diagram of the inverter unit provided with the conventional ground fault detection part.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram of an inverter unit including a ground fault detection unit 100 according to a first embodiment. The illustrated inverter unit 1 is configured to include a transformer 10, a converter unit 30, a smoothing unit 40, an inverter unit 60, a three-phase shielded cable 70, a motor 80, a ground fault detection unit 100, and the like.

  Converter unit 30 is formed of a rectifying diode (not shown) or a plurality of switching elements (not shown), and converts the AC voltage output from transformer 10 into a DC voltage by controlling the gate voltage of the switching elements. .

  The output voltage of the converter unit 30 is output to P (positive electrode) and N (negative electrode), and is supplied to the smoothing unit 40 and the inverter unit 60 connected between P and N.

  The smoothing unit 40 is configured to include the smoothing capacitor C1, and smoothes the DC voltage (pulsating current) output from the converter unit 30.

  The inverter unit 60 is configured by a three-phase inverter, and the inverter of each phase is configured by a plurality of switching elements (for example, IGBTs), and by controlling the gate timing of turning on / off the gates of the switching elements, The DC voltage output from converter unit 30 via smoothing unit 40 is converted into an AC voltage (here, a three-phase AC voltage) for driving motor M (load).

  The three-phase shielded cable 70 is composed of three independent shielded cables. The output terminal of the inverter unit 60 and the power input terminal of the motor 80 are connected to each other and used as a cable for supplying power.

  The inverter unit 60 is composed of a three-phase inverter, and the shield cable is composed of a three-phase shield cable 70. The output terminal side shield wire of the inverter unit 60 and the power input terminal side shield wire of the motor 80 are each for three phases Commonly connected.

  The power input terminal side shield wire 71b of the motor 80 commonly connected to the three phases is connected to the ground terminal G2 of the motor 80 main body.

  The ground terminal G2 of the motor 80 main body, the output terminal side shield wire 71a of the inverter unit 60 commonly connected to three phases, and the in-inverter ground bus bar 61 are connected by the ground wire 74. G2 is not grounded (not grounded).

  The ground terminal G1 of the in-inverter ground bus bar 61 is grounded.

In such a connection form, the zero phase current (ground fault current) flowing through the output terminal side shield wire 71a of the inverter unit 60 commonly connected to the three phases is detected by the current sensor 90. In the present embodiment, the ground In order to detect a winding current, a current sensor 90 is disposed between the ground terminal G2 of the motor 80 main body and the output terminal side shield wire 71a of the inverter unit 60, and a zero phase current of the motor 80 is detected.

  The detection signal of the zero-phase current detected by the current sensor 90 in this manner is input to the ground fault detection unit 100.

  The ground fault detection unit 100 includes an absolute value generation unit 101, a first-order lag filter unit 102, a reference value setting unit 103, a comparator 104, and the like.

  The absolute value generation unit 101 generates an absolute value of the zero-phase current detected by the current sensor 90.

  The first-order lag filter unit 102 cuts high frequency components from the absolute value signal of the zero-phase current generated by the absolute value generation unit 101.

  The comparator 104 compares the reference value set by the reference value setting unit 103 with the absolute value signal of the zero phase current generated by cutting the high frequency component by the first order lag filter unit 102. As a result of the comparison, when the absolute value of the zero phase current exceeds the reference value, the ground fault detection signal 104a is output.

  FIG. 2 is a diagram for explaining the operation of the ground fault detection unit 100 in FIG. 1 when a ground fault occurs. Explain the method of detecting the ground fault current Ign (n: 1 to 5) when a ground fault 73 occurs in which one phase (for example, W phase) in the illustrated three-phase shielded cable contacts the shield wire (ground wire) Do.

(1) Until just before the occurrence of a ground fault, the PWM (Plus Width Modulation) control unit (not shown) of the switching elements Q1 to Q6 specifies the gate terminals G1 to G6 of the switching elements Q1 to Q6. The on / off control is performed along with the on / off control at the timing of.

(2) In this state, when the W-phase ground fault 73 is generated, a ground current Ig1 flows in the direction of the arrow when the switching element Q5 is turned on from the high voltage terminal of the smoothing capacitor C1.

(3) The ground fault current Ig1 flows through the illustrated path, and the ground fault current Ig2 flows toward the ground fault occurrence point in the W phase of the three-phase shielded cable.

(4) The ground fault current Ig2 flows from the ground fault occurrence point through the shield wire 71b toward the ground bus side in the inverter.

(5) The ground fault current Ig4 passes through the shield wire 71a to become the ground fault current Ig5 and is returned to the power supply source. The ground fault current Ig5 is detected by the current sensor 90.

(6) The ground fault current Ig5 passes through the U-phase and V-phase electrostatic capacitance (floating capacitance) C2 in the three-phase shielded cable and becomes the ground fault current Ig6 when the switching elements Q2 and Q4 are on. The low voltage of the smoothing capacitor C1 Return to the terminal side.

(7) The ground fault current Ig5 detected by the current sensor 90 has been described by way of example when the W phase voltage is a positive voltage, but it may be a negative voltage. An absolute value is generated. In the present embodiment, the magnitude of the ground fault current is an important factor, but the polarity is not an important factor.

(8) A high frequency current is superimposed on the absolute value signal of the ground fault current detected in (7), and in order to prevent erroneous detection of the magnitude of the ground fault current by the high frequency current, a first-order delay The filter unit 102 cuts high frequency components from the absolute value signal of the ground fault current.

(9) The comparator 104 compares the reference value set by the reference value setting unit 103 with the absolute value signal of the ground fault current generated by cutting the high frequency component by the first-order lag filter unit 102.

  The reference value setting unit sets the reference value by adding a predetermined allowable value to the absolute value of the zero-phase current detected by the ground fault detection unit 100 for the zero-phase current value of the operation initial value of the inverter unit 60. Do.

  As a result of the comparison, when the absolute value of the ground fault current exceeds the reference value, the ground fault detection signal 104a is output.

  As described above, according to the embodiment of the present invention, the inverter unit 60 and the motor 80 are connected by the three-phase shield cable 70, and the zero-phase current flowing in the shield wire is monitored to obtain a current sensor with a small capacity. Can provide a ground fault detection device of a voltage type inverter capable of detecting a ground fault.

C1 Smoothing capacitor C2 Capacitance of power cable Ig1 to Ig4 Zero phase current (ground current)
G1 Ground terminal of ground conductor in inverter G2 Ground terminal of motor body 10 Transformer 20 Shield cable 30 Converter unit 40 Smoothing unit 50 Ground fault detection unit 60 Inverter unit 61 Ground conductor in inverter 70 Three-phase shield cable 71, 71a, 71b Shield Wire 73 Ground fault 74 Ground wire 80 Motor 90 Current sensor 100 Ground fault detection unit 101 Absolute value generation unit 102 First-order lag filter unit 103 Reference value setting unit 104 Comparator

Claims (4)

A ground fault detection device for a voltage type inverter, wherein an output terminal of an inverter unit and a power input terminal of a motor are connected by a shield cable to drive the motor,
The power input terminal side shield wire of the motor is connected to the ground terminal of the motor body,
Connecting the ground terminal of the motor body to the output terminal side shield wire of the inverter unit and the ground conductor in the inverter with a ground wire;
Although the ground terminal of the ground bus bar is grounded, the ground terminal of the motor body is not grounded,
A current sensor for detecting a zero-phase current flowing through an output terminal side shield line of the inverter unit;
A ground fault detection unit that monitors a zero-phase current detected by the current sensor and detects a ground fault;
A ground fault detection device for a voltage type inverter, comprising: A ground fault detection device for a voltage type inverter, wherein an output terminal of an inverter unit and a power input terminal of a motor are connected by a shield cable to drive the motor,
The inverter unit is configured by a three-phase inverter, the shield cable is configured by a three-phase shield cable, and the output terminal side shield wire of the inverter unit and the power input terminal side shield wire of the motor are commonly connected for three phases. And
The power input terminal side shield wire of the motor commonly connected to the three phases is connected to the ground terminal of the motor body, and the output terminal of the inverter unit commonly connected to the ground terminal of the motor body by three phases Connect the side shield wire and the in-inverter ground bus bar with a ground wire,
Although the ground terminal of the ground bus bar is grounded, the ground terminal of the motor body is not grounded,
A current sensor for detecting a zero-phase current flowing through an output terminal side shield wire of the inverter unit commonly connected to the three phases;
A ground fault detection unit that monitors a zero-phase current detected by the current sensor and detects a ground fault;
A ground fault detection device for a voltage type inverter, comprising: The ground fault detection unit
An absolute value generation unit that generates an absolute value of the zero-phase current detected by the current sensor;
A first-order lag filter unit for cutting a high frequency component from the absolute value signal of the zero phase current generated by the absolute value generation unit;
A comparator configured to compare the reference value set by the reference value setting unit and the absolute value signal of the zero-phase current generated by cutting the high frequency component by the first-order lag filter unit;
The ground of the voltage type inverter according to claim 1 or 2, wherein a ground fault detection signal is output when an absolute value of the zero phase current exceeds the reference value as a result of comparison by the comparator. Fault detection device. The reference value setting unit
A predetermined allowable value is added to the absolute value of the zero-phase current detected by the ground fault detection unit to set the reference value by setting the zero-phase current value of the operation initial value of the inverter unit to the absolute value. The earth fault detection apparatus of the voltage type inverter as described.